Creating and adding a texture to a material (blender 2.8)
If you want to add a texture to any material, simply go in to your shading window. 
--> choose add (shift+A)--> image texture --> plug that in to a principled BSDF tats connected to the material output. 
After that you can simply open up the texture you want and enyoy yore new texture. 

P.S look upp some youtub tutorials on the topic